The present invention relates to a computer monitoring device which monitors whether a computer provided at a power window system of a vehicle or the like operates normally.
Conventionally, in a system using a microcomputer in which a battery is a power supply, when the microcomputer is not used, the microcomputer enters a standby mode and the execution of a program is stopped in order to reduce electricity consumption of the battery. Further, a microcomputer monitoring circuit (watchdog circuit) is provided in the system using the microcomputer. The microcomputer monitoring circuit monitors a state of the microcomputer by the output of a predetermined signal (e.g., a signal which is generated on the basis of a clock signal and will be hereinafter referred to as xe2x80x9cclock signalxe2x80x9d) from the microcomputer. When the clock signal is not detected, the microcomputer monitoring circuit determines that the state of the microcomputer is not normal and outputs a signal which restarts the microcomputer (hereinafter, xe2x80x9crestarting signalxe2x80x9d).
On the other hand, because the microcomputer stops the output of the above-described clock signal by entering the standby mode, the microcomputer monitoring circuit outputs the restarting signal. As a result, the microcomputer which is supposed to enter the standby mode is restarted.
In order to prevent the restarting of the microcomputer which is supposed to enter the standby mode, when the microcomputer monitoring circuit detects a signal which is output when the microcomputer enters the standby mode (hereinafter, xe2x80x9cstandby signalxe2x80x9d), the microcomputer monitoring circuit also enters the standby mode. Namely, when the standby signal is detected, the microcomputer monitoring circuit enters the standby mode and stops the monitoring function of the microcomputer.
An example of a system which includes the microcomputer and the microcomputer monitoring circuit is a power window system of a vehicle. In this power window system, a microcomputer controls a relay or the like and operates a motor for raising and lowering a door glass in accordance with a switch operation. At this time, a microcomputer monitoring circuit monitors an operating state of the microcomputer in order to prevent the control of the motor from being disabled due to runaway or the like of the microcomputer. When it is determined that the microcomputer does not operate normally, a restarting signal is output to the microcomputer.
On the other hand, the power window system includes a microcomputer control system and an SW control system (direct control by a switch) so as to control the motor in accordance with the switch operation. The motor is usually controlled by the microcomputer control system. When the microcomputer enters the standby mode or it is determined by the operating state of the microcomputer monitoring circuit that the operation of the microcomputer fails, the motor is controlled by the SW control system. In this way, the motor can be controlled even if the microcomputer does not operate normally.
By the way, when a microcomputer port or an input terminal of the microcomputer monitoring circuit fails, the standby signal may be input to the microcomputer monitoring circuit by mistake. In this case, even when the microcomputer becomes abnormal and the restarting signal is output, since the microcomputer monitoring circuit detects the standby signal, the microcomputer monitoring circuit enters the standby mode and stops monitoring of the microcomputer which is a fundamental function.
In order to prevent this, a microcomputer monitoring circuit has been proposed which, when a restarting signal is output, does not enter a standby mode even if a standby signal is detected. This microcomputer monitoring circuit enters the standby mode when the microcomputer monitoring circuit detects the signal entering the standby mode from the time in which a predetermined signal output from the microcomputer is not detected to the time in which a signal restarting the microcomputer is output. As a result, when the microcomputer becomes abnormal and the predetermined signal is not detected, even if the signal entering the standby mode is detected, the microcomputer monitoring circuit can output the signal which urges the restarting of the microcomputer without stopping the monitoring function.
However, in this computer monitoring device (microcomputer monitoring circuit), when the microcomputer is restarted or the like in a state in which a wrong standby signal is detected and the device detects a predetermined signal which is output from the microcomputer at the time of normal operation thereof, it is determined that the microcomputer operates normally. At this time, the computer monitoring device enters the standby mode since the standby signal is detected. Thus, there is a drawback in that the monitoring of the microcomputer is stopped.
The present invention was developed in light of the above circumstances, and the object thereof is to provide a computer monitoring device which does not enter a standby mode even if a standby signal is input by mistake.
In order to solve the above-described problems, the present invention comprising: starting means which outputs a starting signal before starting a computer, the starting means outputting a starting signal to the computer when a first signal, which is output from the started computer in a predetermined cycle, is stopped for a predetermined period of time; start stopping means which stops an operation of the starting means when a second signal, which is output from the computer with a predetermined timing, is input; start operation determination means which outputs a third signal, which urges stopping of an operation of the start stopping means, due to inputting of the starting signal, the start operation determination means stopping outputting of the third signal by the first signal which is output from the computer only when the second signal is not detected; and operation monitoring means which stops outputting of the input second signal to the start stopping means when the start operation determination means outputs the third signal.
In accordance with the present invention, the starting means outputs the starting signal after a predetermined period of time has passed since the first signal, which is output from the computer in a predetermined cycle, is not input. When the second signal, which is output from the computer at the time of entering the standby mode, is detected, the start stopping means stops the operation of the starting means. As a result, since the computer outputs the second signal when entering the standby mode, even if the computer which enters the standby mode stops the output of the first signal, the computer is not started by the starting signal.
On the other hand, the start operation determination means outputs the third signal due to the input of the starting signal and stops the output of the third signal when the first signal is detected before the second signal is detected. Further, the operation monitoring means outputs the second signal to the start stopping means due to the detection of the second signal and, when the third signal is detected, the output of the second signal to the start stopping means is stopped.
In this way, the starting means can be operated on the basis of the first signal and outputs the starting signal if the computer stops the output of the first signal. Accordingly, when the computer is started and the second signal is input by mistake, the computer can be monitored due to the output of the third signal. When the first signal is not input, the starting signal for operating the computer normally can be output.
Further, in the present invention, when the start operation determination means detects the first signal in a state in which the second signal is not detected, the output of the third signal is stopped. Consequently, the state in which the microcomputer operates or not can be monitored by the output of the start operation determination means and the operation monitoring means.
Namely, when the computer operates normally, it can be determined that the second and the third signals are not detected. Further, when only the second signal output from the operation monitoring means is detected, it can be determined that the computer enters the standby mode. When the third signal output from the start operation determination means is detected, it can be determined that the computer is restarted.
Therefore, when the present invention is applied, for example, to monitor the computer of the power window system, only when the second signal or the third signal is not detected, it can be determined that the computer operates normally. Thus, switching between the microcomputer control system and the SW control system may be effected on the basis of this result of determination.